Method for producing aromatic nitrile compound and method for producing carbonic acid ester

ABSTRACT

Provided is a method for regenerating an aromatic amide compound into a corresponding aromatic nitrile compound, the method realizing a dehydration reaction of providing a target compound selectively at a high yield, with generation of a by-product being suppressed. Also provided is a method for producing an aromatic nitrile compound that decreases the number of steps of the dehydration reaction and significantly improves the reaction speed even at a pressure close to normal pressure. In addition, the above-described production method is applied to a carbonate ester production method to provide a method for producing a carbonate ester efficiently. The above-described methods are realized by a method for producing an aromatic nitrile compound including a dehydration reaction of dehydrating an aromatic amide compound, in which the dehydration reaction uses, as a solvent, any of 1,2-dimethoxybenzene, 1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 16/470,817, which is a National Phase applicationof International Application No. PCT/JP2017/042936, filed on Nov. 30,2017, which claims the benefit of Japanese Patent Application No.2016-248094, filed on Dec. 21, 2016. The entire disclosure of each ofthe above-identified applications, including the specification,drawings, and claims, is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a method for producing an aromaticnitrile compound such as cyanopyridine or the like, and a method forproducing a carbonate ester.

BACKGROUND ART

“Carbonate ester” is a generic name of a compound obtained as a resultof one atom or two atoms among two hydrogen atoms of carbonic acid,CO(OH)₂, being substituted with an alkyl group or an aryl group, and hasa structure of RO—C(═O)—OR′ (R and R′ each represent a saturatedhydrocarbon group or an unsaturated hydrocarbon group).

A carbonate ester is used as an additive, for example, a gasolineadditive for improving the octane value and a diesel fuel additive fordecreasing the amount of particles in exhaust gas. A carbonate ester isalso used as, for example, an alkylation agent, a carbonylation agent, asolvent or the like for synthesizing resins or organic compounds such aspolycarbonate, urethane, pharmaceutical drugs, agricultural chemicals orthe like, a material of an electrolytic solution of lithium ion cells, amaterial of lubricant oil, or a material of an oxygen absorber for rustinhibition of boiler pipes. As can be seen, a carbonate ester is a veryuseful compound.

According to a conventionally mainstream method for producing acarbonate ester, phosgene, which is used as a source of a carbonyl, isdirectly reacted with an alcohol. Phosgene used in this method is highlyhazardous and highly corrosive, and therefore, needs extreme cautionwhen being handled, for example, transported or stored. It is highlycostly to control and manage, and guarantee the safety of, productionfacilities of phosgene. According to this method, the materials andcatalysts used for producing a carbonate ester contain halogen such aschlorine or the like, and the produced carbonate ester contains a traceamount of halogen, which is not removed by a simple purification step.When the carbonate ester is used for a gasoline additive, a light oiladditive or an electronic material, such halogen may undesirably causecorrosion. Therefore, a thorough purification step is indispensable todecrease the trace amount of halogen present in the carbonate ester tothe level of an extremely trace amount. In addition, recently,administrative offices provide a strict administration guidance and donot permit new establishment of production facilities using this methodbecause this method uses phosgene, which is highly hazardous to thehuman body. In such a situation, a new production method of a carbonateester that does not use phosgene is strongly desired.

There is another known method for producing a carbonate ester. Accordingto this method, a carbonate ester is directly synthesized from analcohol and carbon dioxide using a heterogeneous catalyst. Regardingthis method, studies had been made on using 2-cyanopyridine orbenzonitrile as a wettable powder to significantly improve theproduction amount and the production speed of the carbonate ester, toallow the reaction to advance easily at a pressure close to normalpressure, and to increase the reaction speed (see Patent Documents 1 and2). However, there was a problem regarding the method for treating orusing benzamide or the like generated as a by-product.

For example, benzamide generated by the reaction of benzonitrile andwater is limited to being usable for some of pharmaceutical andagrochemical intermediates. Therefore, regarding the method of producinga carbonate ester using benzonitrile as a wettable powder, benzamidegenerated as a by-product is desired to be regenerated into benzonitrileand reused. It is now an issue to realize a regeneration reaction with ahigh level of selectivity (because it is considered that if a by-productis generated, benzonitrile is not easily used as a wettable powder) anda high yield (because if the yield is low, benzamide remains in a largeamount, which increases the amount of work, namely, work load, ofseparating benzamide and benzonitrile from each other).

In light of the above-described situation where regeneration ofbenzamide or the like into benzonitrile or the like involves problems,there is a known method for realizing the regeneration with no use of astrong reagent and with the generation of a by-product being suppressed(Patent Document 3).

However, according to this method, generation of nitrile by dehydrationof an amide compound requires 400 hours and thus is not well balancedwith, namely, is not usable together with, a carbonate ester synthesisreaction, which requires only 24 hours. This method also has a problemthat steps of extraction, infiltration and the like are necessary forsolid-liquid separation of a catalyst, which increases the number ofproduction steps and complicates the production process.

CITATION LIST Patent Literature

Patent Document 1: Japanese Laid-Open Patent Publication No. 2010-77113

Patent Document 2: Japanese Laid-Open Patent Publication No. 2012-162523

Patent Document 3: WO2015/099053

SUMMARY OF INVENTION Technical Problem

In light of the above-described technological problems, an object of thepresent invention is to provide a method for regenerating an aromaticamide compound, for example, pyridine carboamide, into a correspondingaromatic nitrile compound, namely, cyanopyridine, the method realizing adehydration reaction of providing a target compound selectively at ahigh yield, with generation of a by-product being suppressed. Anotherobject of the present invention is to provide a method for producing anaromatic nitrile compound that decreases the number of steps of thedehydration reaction and significantly improves the reaction speed toshorten the reaction time even at a pressure close to normal pressure.

A still another object of the present invention is to apply theabove-described method for producing an aromatic nitrile compound to acarbonate ester production method to provide a method for producing acarbonate ester efficiently.

Solution to Problem

In order to achieve the above-described objects, the present inventorsmade studies on a method for producing an aromatic nitrile compound suchas cyanopyridine or the like by dehydration of an aromatic amidecompound. More specifically, the present inventors studied reactionconditions for dehydrating an aromatic amide compound, and as a result,found the following. In the case where a predetermined solvent is used,a process of dehydration reaction is realized by which the reactionspeed is significantly improved to shorten the reaction time, the targetcompound is obtained selectively at a high yield while generation of aby-product is suppressed, and the aromatic nitrile compound is easilyrecovered. The present inventors also found the following. Since theprocess of dehydration reaction conceived by the present inventors doesnot need solid-liquid separation of a catalyst, the number of steps ofthe dehydration reaction is decreased. Preferably, the dehydrationreaction is advanced in a state where the solvent is boiled.

By the present invention described above, the speed of regenerating anaromatic nitrile compound by a dehydration reaction of an aromatic amidecompound, and the speed of synthesizing a carbonate ester from CO₂ andan alcohol using the aromatic nitrile compound, are now well balanced.Namely, the dehydration reaction and the carbonate ester synthesisreaction are now established as a series of commercial processes. Basedon this, the present inventors also made studies on applying theabove-described knowledge to a method for producing a carbonate ester.Namely, the present inventors have found the following regarding thecarbonate ester production method of directly synthesizing a carbonateester from an alcohol and carbon dioxide. In the case where, forexample, a solvent having a boiling point higher than that of thearomatic amide compound is used, the number of steps of the reaction isdecreased and the method is simplified with no need of solid-liquidseparation of a catalyst. The present inventors have confirmed that sucha carbon ester synthesis method may be combined with the dehydrationreaction, using a predetermined solvent, of an aromatic amide compoundto generate an aromatic nitrile compound, so that a splendid effect isprovided. The gist of the present invention is as follows.

(1) A method for producing an aromatic nitrile compound, comprising:

a dehydration reaction of dehydrating an aromatic amide compound;

wherein the dehydration reaction uses a solvent containing one or aplurality of substances selected from 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene.

(2) The method for producing an aromatic nitrile compound according to(1) above, wherein a total amount of the one or the plurality ofsubstances selected from 1,2-dimethoxybenzene, 1,3-dimethoxybenzene and1,3,5-trimethoxybenzene is 5% by weight or greater with respect to thesolvent.

(3) The method for producing an aromatic nitrile compound according to(1) or (2) above, wherein the solvent is formed of only the one or theplurality of substances selected from 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene.

(4) The method for producing an aromatic nitrile compound according to(1) or (2) above, wherein the solvent is a mixed solvent furthercontaining a compound having a boiling point that is higher than theboiling point of the aromatic nitrile compound and the boiling point ofwater and is lower than the boiling point of the aromatic amidecompound.

(5) The method for producing an aromatic nitrile compound according toany one of (1) through (4) above, wherein the solvent is used in anamount larger than, or equal to, an equimolecular amount of the aromaticamide compound.

(6) The method for producing an aromatic nitrile compound according toany one of (1) through (5) above, wherein the dehydration reaction isperformed in a state where the solvent is boiled.

(7) The method for producing an aromatic nitrile compound according toany one of (1) through (6) above, wherein the dehydration reaction isperformed under the condition of normal pressure or a reduced pressure.

(8) The method for producing an aromatic nitrile compound according toany one of (1) through (7) above, wherein a reaction solution of thedehydration reaction has a temperature of 170° C. or higher and lowerthan 230° C.

(9) The method for producing an aromatic nitrile compound according toany one of (1) through (8) above, wherein the aromatic amide compoundcontains pyridine carboamide, and the aromatic nitrile compound containscyanopyridine.

(10) The method for producing an aromatic nitrile compound according toany one of (1) through (9) above, wherein the dehydration reaction usesa catalyst containing cesium.

(11) A method for producing an aromatic nitrile compound, comprising:

a dehydration reaction of dehydrating an aromatic amide compound;

wherein the dehydration reaction uses a solvent containing one or aplurality of substances selected from 1,2,3,4-tetrahydronaphthalene,1,2-dimethoxybenzene, 1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene,and a catalyst containing cesium.

(12) A method for producing a carbonate ester, comprising:

a first reaction step including a carbonate ester generation reaction ofreacting an alcohol and carbon dioxide in the presence of an aromaticnitrile compound to generate a carbonate ester and water, and ahydration reaction of hydrating the aromatic nitrile compound with thegenerated water to generate an aromatic amide compound; and

a second reaction step of, after the aromatic amide compound isseparated from a reaction system of the first reaction step,regenerating the aromatic amide compound into an aromatic nitrilecompound by a dehydration reaction of dehydrating the aromatic amidecompound in a solvent containing one or a plurality of substancesselected from 1,2-dimethoxybenzene, 1,3-dimethoxybenzene and1,3,5-trimethoxybenzene;

wherein at least a part of the aromatic nitrile compound regenerated inthe second reaction step is used in the first reaction step.

(13) The method for producing a carbonate ester according to (12) above,wherein a total amount of the one or the plurality of substancesselected from 1,2-dimethoxybenzene, 1,3-dimethoxybenzene and1,3,5-trimethoxybenzene is 5% by weight or greater with respect to thesolvent.

(14) The method for producing an aromatic nitrile compound according to(12) or (13) above, wherein the solvent is formed of only the one or theplurality of substances selected from 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene.

(15) The method for producing a carbonate ester according to (12) or(13) above, wherein the solvent is a mixed solvent further containing acompound having a boiling point that is higher than the boiling point ofthe aromatic nitrile compound and the boiling point of water and islower than the boiling point of the aromatic amide compound.

(16) The method for producing a carbonate ester according to any one of(12) through (15) above, wherein the solvent is used in an amount largerthan, or equal to, an equimolecular amount of the aromatic amidecompound.

(17) The method for producing a carbonate ester according to any one of(12) through (16) above, wherein the dehydration reaction is performedin a state where the solvent is boiled.

(18) The method for producing a carbonate ester according to any one of(12) through (17) above, wherein the dehydration reaction is performedunder the condition of normal pressure or a reduced pressure.

(19) The method for producing a carbonate ester according to any one of(12) through (18) above, wherein a reaction solution of the dehydrationreaction has a temperature of 170° C. or higher and lower than 230° C.

(20) The method for producing a carbonate ester according to any one of(12) through (19) above, wherein the aromatic amide compound containspyridine carboamide, and the aromatic nitrile compound containscyanopyridine.

(21) The method for producing a carbonate ester according to any one of(12) through (20) above, wherein the dehydration reaction uses acatalyst containing cesium.

(22) The method for producing a carbonate ester according to any one of(12) through (21) above, wherein the carbonate ester generation reactionuses a catalyst containing cerium.

(23) The method for producing a carbonate ester according to any one of(12) through (22) above, wherein the alcohol contains an alcohol havinga carbon number of 1 through 6.

(24) A method for producing a carbonate ester, comprising:

a first reaction step including a carbonate ester generation reaction ofreacting an alcohol and carbon dioxide in the presence of an aromaticnitrile compound to generate a carbonate ester and water, and ahydration reaction of hydrating the aromatic nitrile compound with thegenerated water to generate an aromatic amide compound; and

a second reaction step of, after the aromatic amide compound isseparated from a reaction system of the first reaction step,regenerating the aromatic amide compound into an aromatic nitrilecompound by a dehydration reaction of dehydrating the aromatic amidecompound in a solvent containing one or a plurality of substancesselected from 1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene by use of a catalystcontaining cesium;

wherein at least a part of the aromatic nitrile compound regenerated inthe second reaction step is used in the first reaction step.

(25) A method for producing a carbonate ester, comprising:

a first reaction step including a carbonate ester generation reaction ofreacting an alcohol and carbon dioxide in the presence of an aromaticnitrile compound to generate a carbonate ester and water, and ahydration reaction of hydrating the aromatic nitrile compound with thegenerated water to generate an aromatic amide compound; and

a second reaction step of, after the aromatic amide compound isseparated from a reaction system of the first reaction step,regenerating the aromatic amide compound into an aromatic nitrilecompound by a dehydration reaction of dehydrating the aromatic amidecompound in a solvent formed of only one or a plurality of substancesselected from 1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene by use of a catalystcontaining cesium;

wherein at least a part of the aromatic nitrile compound regenerated inthe second reaction step is used in the first reaction step.

Advantageous Effects of Invention

According to the present invention as described above, an aromaticnitrile compound such as cyanopyridine or the like is efficientlyproduced (regenerated) from an aromatic amide compound such as pyridinecarbonamide (picolinamide, nicotinamide or the like), benzamide or thelike. More specifically, the dehydration reaction of an aromatic amidecompound for the regeneration is performed to obtain a target compoundselectively at a high yield, while generation of a by-product issuppressed. Even under mild reaction conditions, for example, at apressure close to normal pressure, the reaction speed is increased.Therefore, according to the present invention, the reaction time of thedehydration reaction of regenerating an aromatic nitrile compound issignificantly shortened as compared with the reaction time required bythe conventional method.

Also according to the present invention, an aromatic nitrile compound isproduced as described above, and as a result, a method for producing acarbonate ester efficiently is realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of device for producing a carbonate ester.

FIG. 2 is a chart showing the state of each of substances at each ofsteps in the production performed by use of the production device shownin FIG. 1.

FIG. 3 is a graph showing the composition of the solvents in the mixedsolvent and the nitrile selectivity (ratio of the amount of the aromaticnitrile compound and the total amount of impurities).

FIG. 4 is a graph showing the ratio of the yields (generation ratios) ofnitrile and pyridine in an example and a comparative example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferable embodiment of the present invention will bedescribed in detail with reference to the attached drawings. In thespecification and the drawings, components having substantially the samefunctions or structures will bear the same reference signs, and the samedescriptions will not be repeated.

<1. Method for Producing an Aromatic Nitrile Compound>

According to a method of the present invention for producing an aromaticnitrile compound, an aromatic nitrile compound such as cyanopyridine orthe like is produced by dehydration of an aromatic amide compound suchas pyridine carboamide (2-pyridine carboamide, 3-pyridine carboamide or4-pyridine carboamide) or the like. According to this method, anaromatic amide compound is subjected to a dehydration reaction in thepresence of, for example, a catalyst containing a carried basic metaloxide and a predetermined solvent to generate an aromatic nitrilecompound.

(Catalyst)

The catalyst usable in the above-described dehydration reactionaccording to the present invention contains an oxide of an alkalinemetal (K, Li, Na, Rb, Cs), which is basic. It is especially preferablethat the catalyst usable in the above-described reaction contains anoxide of at least one of Na, K, Rb and Cs (cesium). A carrier of thecatalyst may be a substance that generally acts as a carrier of acatalyst. As a result of studies made on various carriers, it has beenfound that a catalyst containing one or two of SiO₂ and ZrO₂ as acarrier exhibits an especially high level of performance.

Examples of methods for producing a catalyst usable for theabove-described dehydration reaction will be described. In the casewhere the carrier is SiO₂, commercially available powdery or sphericalSiO₂ is usable. Preferably, SiO₂ is sized to 100 mesh (0.15 mm) or lessso that an active metal is uniformly carried, and is pre-baked at 700°C. for 1 hour in the air in order to remove the moisture. There arevarious types of SiO₂ of various properties. SiO₂ having a largersurface area is more preferable because as the surface area is larger,the active metal is dispersed more highly and the generation amount ofan aromatic nitrile compound is increased. Specifically, a surface areaof 300 m² or greater is preferable. It should be noted that there may bea case where the surface area of the prepared catalyst is smaller thanthe surface area of SiO₂ alone as a result of, for example, mutualaction of SiO₂ and the active metal. In this case, the surface area ofthe produced catalyst is preferably 150 m² or greater. The metal oxideacting as an active species may be carried by an impregnation methodsuch as an incipient wetness method, an evaporation-to-dryness method orthe like.

A metal salt acting as a precursor of the catalyst merely needs to bewater-soluble. Examples of usable alkaline metal salts include variouscompounds such as carbonate, hydrogencarbonate, chloride, nitrate,silicate and the like. An aqueous solution of a precursor formed of abasic metal is impregnated with a carrier, then is dried and baked. Theresultant substance is usable as a catalyst. The baking temperature,which depends on the precursor used, is preferably 400 to 600° C.

The amount of the catalyst to be carried may be set appropriately. Forexample, the amount of an alkaline metal oxide to be carried, convertedto the metal, is set to preferably about 0.1 to 1.5 mmol/g, andespecially preferably about 0.1 to 1 mmol/g, with respect to the totalweight of the catalyst. In the case where the amount to be carried islarger than such a value, the activity may undesirably be decreased. Theamount of the catalyst to be used for the reaction may be setappropriately.

A catalyst preferably usable in the present invention includes a carrierformed of one or two of SiO₂ and ZrO₂ and only an alkaline metaloxide(s) of one, or at least two, types carried by the carrier. Thecatalyst may contain, in addition to the above-described elements,unavoidable impurities incorporated in a step of, for example, producingthe catalyst. Nonetheless, it is desirable to avoid incorporation ofimpurities to a maximum possible degree.

The catalyst, usable in the present invention, including a metal oxideacting as an active species and carried by the carrier may be in theform of powder or a molded body. In the case of being a molded body, thecatalyst may be spherical, pellet-like, cylindrical, ring-shaped,wheel-shaped, granular or the like.

(Reaction Format and Reaction Vessel)

With the method according to the present invention for producing anaromatic nitrile compound using the catalyst, there is no specificlimitation on the form of the reaction. A flow reactor such as a batchreactor, a semi-batch reactor, a continuous tank reactor, a tube reactoror the like is usable. For the catalyst, a fixed bed, a slurry bed orthe like is usable.

With the method for producing an aromatic nitrile compound according tothe present invention, it is desirable to perform the reaction toproduce an aromatic nitrile compound while removing by-product watergenerated by the dehydration reaction. For example, it is desirable toperform reflux or distillation or to provide a dehydration agent such aszeolite or the like in the system, so that the reaction is performedwhile the by-product water is removed. As a result of the active studiesmade by the present inventors, it has been found that the generationamount of an aromatic nitrile compound may be increased as follows byuse of, for example, a reaction distillation device having adecompression device attached thereto. A catalyst, an aromatic amidecompound and a solvent are put into a reaction tube, the pressure isreduced to control the temperature of the reaction solution, and thesolvent is refluxed to distill the reaction liquid to separate andremove the by-product water from the system.

(Solvent)

A solvent usable for the above-described dehydration reaction containsone or a plurality of substances selected from 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene. In addition to theabove-listed three substances, 1,2,3,4-tetrahydronaphthalene may beincluded in a list of usable solvents. In the dehydration reaction usinga solvent containing one or a plurality of substances selected from1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene as described above, itis preferable to use a catalyst containing cesium.

For the dehydration reaction, it is preferable to use a solvent formedonly of one or a plurality of above-listed substances, namely,1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene (hereinafter, thesefour substances will each be referred to as a “specific solventcompound). Alternatively, a mixed solvent containing another compound isalso usable.

The mixed solvent usable for the dehydration reaction may containanother compound in addition to any of the four specific solventcompounds listed above or any of the three specific solvent compoundslisted above other than 1,2,3,4-tetrahydronaphthalene. In the case wherethe mixed solvent contains a compound other than the specific solventcompounds, it is especially preferable that the compound has a boilingpoint that is higher than the boiling point of the aromatic nitrilecompound to be produced (regenerated) and also the boiling point ofwater and is lower than the boiling point of the aromatic amide compoundto be dehydrated. The compound contained in the mixed solvent as acompound other than the specific solvent compounds is, for example,diphenylether. Diphenylether has a high boiling point of about 259° C.and suppresses the evaporation amount of the mixed solvent containingthe specific solvent compound(s), and thus advances the dehydrationreaction efficiently. Therefore, diphenylether is preferably usable.

With respect to the mixed solvent used for the dehydration reaction, thetotal amount of the four specific solvent compounds (or the threespecific solvent compounds other than 1,2,3,4-tetrahydronaphthalene) ispreferably 5% by weight or greater, more preferably 20% by weight orgreater, and especially preferably 40% by weight or greater. In the casewhere the total amount of the specific solvent compounds is adjusted tobe within such a range, the selectivity (mol %) of the aromatic nitrilecompound represented by expression (1) below (ratio of the amount of thegenerated aromatic nitrile compound with respect to the amount of thereacted aromatic amide compound; hereinafter, this selectivity will alsobe referred to as “nitrile selectivity”; regarding the details, refer toFIG. 3 described below) is improved while another compound having apreferable property such as, for example, a preferable boiling point isallowed to be contained in the solvent.[Expression 1]Amount of aromatic nitrile compound (mol)/(amount of pre-reactionaromatic amide compound (mol)−amount of post-reaction aromatic amidecompound (mol))×100  expression 1

The amount of the solvent to be used for the dehydration reaction is,for example, greater than, or equal to, the equimolecular amount of thearomatic amide compound, which is the target of the dehydrationreaction. If the amount of the solvent to be used is too small, thespeed of the dehydration reaction is decreased to increase the amount ofby-products. Therefore, the amount of the solvent to be used for thedehydration reaction is preferably five times the molar amount, morepreferably 15 times the molar amount, and especially preferably 25 timesthe molar amount, of the aromatic amide compound.

(Conditions for the Dehydration Reaction)

It is preferable that the reaction conditions are selected from thepoints of view of the dehydration reaction speed, the boiling point ofthe solvent, the by-product generated by the reaction such as pyridineor the like, the economic efficiency and the like. In the case where amixed solvent is used in the dehydration reaction, it is difficult toaccurately define and measure the boiling point of the solvent. It isgenerally preferable that the boiling point of the mixed solvent ishigher than the boiling point of the aromatic nitrile compound and theboiling point of water and is lower than the boiling point of thearomatic amide compound. In the case where a mixed solvent having aboiling point in such a range is used in the dehydration reaction, theevaporation of the solvent is suppressed while water, which is aby-product, is efficiently removed to the outside of the system asdescribed below in detail.

The usual reaction conditions for the method for producing an aromaticnitrile compound according to the present invention may be as follows.The temperature of the reaction solution is 170° C. to 230° C.; thepressure is normal pressure (101.3 (kPa) (760 Torr) to reduced pressure(13.3 (kPa) (100 Torr)); and the time is several hours to about 100hours. The reaction conditions are not limited to the above.

For example, the temperature of the reaction solution is preferably 180to 228° C., and more preferably 190 to 210° C. The reaction pressure ispreferably 1.33 to 60 (kPA) (10 to 450 Torr), and more preferably 13.3to 53.3 (kPa) (100 to 400 Torr). The reaction time is preferably 4 to 24hours, and more preferably 8 to 24 hours.

In the case where a molecular sieve is used as the dehydration agent,there is no specific limitation on the type or the shape of themolecular sieve. For example, a general molecular sieve that has a highwater absorption rate such as 3A, 4A, 5A or the like and is spherical orpellet-like is usable. For example, Zeolum produced by Tosoh Corporationis usable. Preferably, the molecular sieve is dried in advance, forexample, at 300 to 500° C. for about 1 hour.

(Example of the Dehydration Reaction)

In the dehydration reaction of the aromatic amide compound, it isconsidered that as shown above, the aromatic amide compound isdecomposed to produce an aromatic carboxylic acid, from which pyridineis produced as a by-product. However, a reaction solution obtained afterthe dehydration reaction performed using the reaction conditionsaccording to the present invention contains an aromatic amide compoundin an unreacted state, an aromatic nitrile compound as a reactionproduct and a solvent, but a by-product such as pyridine shown in theabove formula or the like is not generated almost at all.

In the case where a specific solvent compound is used as a solvent inthe dehydration reaction described above, an aromatic nitrile compoundis selectively produced in a short time as described below in detail.Therefore, any of the four specific solvent compounds is preferablyusable for the dehydration reaction.

In the case where, for example, 1,3,5-trimethoxybenzene, among thespecific solvent compounds, is used in the above-described dehydrationreaction, the reaction phase is entirely liquid, except that thecatalyst is solid, for the reason that the melting points of thesubstances are 110° C. (2-picolinamide), 24° C. (2-cyanopyridine), 19°C. (cyanopyrazine) and 50 to 53° C. (1,3,5-trimethoxybenzene), and theboiling points of the substances are 275° C. (2-picolinamide), 232° C.(2-cyanopyridine), 100° C. (water) and 255° C.(1,3,5-trimethoxybenzene). A reaction distillation device having adecompression device attached thereto is used, the distillation columnis heated to have a temperature that is higher than the boiling point ofwater at the reaction pressure and is lower than the boiling point of1,3,5-trimethoxybenzene at the reaction pressure, and the reactionsolution is heated to have a temperature that is higher than, or equalto, the boiling point of 1,3,5-trimethoxybenzene at the reactionpressure and is lower than the boiling point of 2-picolinamide at thereaction pressure. In this manner, 1,3,5-trimethoxybenzene partiallygasified in the reaction system is cooled by a cooling device andreturns to the reaction tube, whereas the by-product water isefficiently separated by distillation from the reaction solution andremoved to the outside of the system. Therefore, a nitrile regenerationreaction advances at high speed, and thus the time of the dehydrationreaction is significantly shortened.

As can be seen, use of, for example, 1,3,5-trimethoxybenzene especiallyallows the dehydration reaction to be advanced efficiently and allowsthe aromatic nitrile compound to be recovered easily. Namely, since theboiling points of the substances present in the post-reaction system aredifferent from each other as described above, the components are easilyseparated from each other by distillation.

It should be noted that even a specific solvent compound having arelatively low boiling point allows an aromatic nitrile compound to beselectively produced in a short time as described above, and thus isconsidered as being suitable to be used for the dehydration reaction.Therefore, in the dehydration reaction using a specific solvent compoundhaving a relatively low boiling point as a solvent, for example, thereaction conditions such as the temperature and the pressure may beappropriately adjusted, or a mixed solvent containing a compound havinga relatively high boiling point together with a specific solventcompound may be used. In this manner, the aromatic amide compound isconverted into an aromatic nitrile compound especially efficiently.

<2. Method for Producing a Carbonate Ester Using an Aromatic NitrileCompound>

As described above, as a result of the dehydration reaction ofregenerating an aromatic amide compound into an aromatic nitrilecompound, the target compound is obtained selectively at a high yieldwith no use of a strong reagent and with the generation of a by-productbeing suppressed. In addition, the reaction speed is significantlyimproved to significantly shorten the reaction time. Therefore, thespeed of regeneration by the dehydration reaction from an aromatic amidecompound into an aromatic nitrile compound, and the speed of carbonateester synthesis from CO₂ and an alcohol using the aromatic nitrilecompound, are now well balanced; namely, the above-describedregeneration and the above-described synthesis may be used together.These reactions may be established as a series of commercial processes.The present inventors applied this knowledge to a carbonate esterproduction method to conceive the following method for producing acarbonate ester,

(First Reaction Step)

A first reaction step of the method for producing a carbonate esteraccording to the present invention includes, for example, directlyreacting an alcohol and carbon dioxide with each other in the presenceof a solid catalyst containing CeO₂ (cerium oxide) or the like and anaromatic nitrile compound to generate a carbonate ester (carbonate estergeneration reaction).

In this step, an alcohol and carbon dioxide are reacted with each other.As a result, a carbonate ester and also water are generated. Thearomatic nitrile compound, which is present in the reaction system, andthe generated water are subjected to a hydration reaction to generate anaromatic amide compound. The generated water is removed from thereaction system or decreased in the amount. Water is removed from thereaction system efficiently as described above, so that the generationof the carbonate ester is promoted. For example, the reaction isexpressed by the following formula.

(Alcohol)

As the alcohol, any one, or two or more, selected from primary alcohol,secondary alcohol and tertiary alcohol are usable. Examples ofpreferable alcohols include methanol, ethanol, 1-propanol, isopropanol,1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol,allylalcohol, 2-methyl-1-propanol, cyclohexanemethanol, benzylalcohol,ethyleneglycol, 1,2-propanediol, and 1,3-propanediol. These alcoholsincrease the yield of the target product and also increase the reactionspeed. The carbonate esters generated by use of the above-listedalcohols are respectively dimethyl carbonate, diethyl carbonate,dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, dipentylcarbonate, dihexyl carbonate, diheptyl carbonate, dioctyl carbonate,dinonane carbonate, diallyl carbonate, di-2-methyl-propyl carbonate,dicyclohexanemethyl carbonate, dibenzyl carbonate, ethylene carbonate,1,2-propylene carbonate, and 1,3-propylene carbonate.

In the case where the obtained carbonate ester is used as a material ofdiallyl carbonate, it is preferable to use an alcohol having a carbonnumber of 1 to 6, and it is more preferable to use an alcohol having acarbon number of 2 to 4.

It is preferable to use a monohydric alcohol or a dihydric alcohol.

(Catalyst Usable for Producing a Carbonate Ester)

In the first reaction step of the method for producing a carbonateester, it is preferable to use one or both of CeO₂ and ZrO₂ as a solidcatalyst. For example, it is preferable to use only CeO₂, only ZrO₂, amixture of CeO₂ and ZrO₂, a solid solution of CeO₂ and ZrO₂, or acomposite oxide of CeO₂ and ZrO₂. It is especially preferable to useonly CeO₂. The mixing ratio of CeO₂ and ZrO₂ in the solid solution orthe composite oxide is basically 50:50, but may be changedappropriately.

The catalyst used in the first reaction step may be in the form ofpowder or a molded body. In the case of being a molded body, thecatalyst may be spherical, pellet-like, cylindrical, ring-shaped,wheel-shaped, granular or the like.

(Carbon Dioxide)

In the present invention, carbon dioxide prepared as industrial gas, orcarbon dioxide separated and recovered from exhaust gas of plantsproducing various products, steel manufacturing plants, power plants orthe like, is usable.

(Solvent in the Carbonate Ester Generation Reaction)

For the carbonate ester generation reaction, it is preferable to use asolvent having a boiling point higher than that of the amide compound tobe produced. More preferably, the solvent in the carbonate estergeneration reaction contains at least one of dialkylbenzene,alkylnaphthalene, and diphenylbenzene. Specific examples of preferablesolvents include barrel process oil B28AN and barrel process oil B30(produced by Matsumura Oil Co., Ltd.), each of which a containscomponent such as dialkylbenzene, alkylnaphthalene, diphenylbenzene orthe like.

(Separation by Distillation)

After the reaction, the obtained substance may be distilled to beseparated into a carbonate ester as a main product, an aromatic amidecompound as a by-product, an unreacted aromatic nitrile compound, and asolid catalyst such as CeO₂ or the like. Thus, the products arerecovered.

(Second Reaction Step)

In a second reaction step according to the present invention, thearomatic amide compound generated as a by-product in the first reactionstep is separated from, preferably, the system obtained after thecarbonate ester generation reaction, and then an aromatic nitrilecompound is produced by a dehydration reaction. The second reaction stepcorresponds to the above-described method for producing the aromaticnitrile compound, and thus will not be described in detail.

(Reuse of the Aromatic Nitrile Compound)

The aromatic nitrile compound regenerated by the second reaction step isreusable for the first reaction step (hydration reaction).

According to the present invention, as described above, a solventcontaining a specific solvent compound is used in the dehydrationreaction of an aromatic amide compound, so that an aromatic nitrilecompound is efficiently regenerated from the aromatic amide compoundwhile generation of a by-product is suppressed. In addition, forexample, the temperature of the reaction solution is adjusted, so thatthe step of solid-liquid separation of the catalyst is made unnecessary,and also the aromatic nitrile compound is easily recovered. In thecarbonate ester generation reaction, a catalyst having a boiling pointhigher than that of aromatic carboamide is used, so that the step ofsolid-liquid separation of the catalyst is made unnecessary. As can beseen, according to the present invention, an aromatic nitrile compoundis selectively regenerated from an aromatic amide compound, and a seriesof reactions are allowed to be advanced while the components areseparated from each other only by distillation without a step ofsolid-liquid separation of the catalyst. Thus, an efficient process asdescribed below in detail is realized.

<3. Device for Producing a Carbonate Ester>

Now, a production device usable in the present invention will bedescribed in detail by way of a specific example. FIG. 1 shows anexample of preferable production device. FIG. 2 schematically shows thestate of each of the substances in each of the steps performed by theproduction device.

(First Reaction Step)

In the first reaction step, a carbonate ester reactor 1 (first reactionportion) is filled with one or both of CeO₂ and ZrO₂ as a solid catalyst(solid phase), alcohol (1-butanol (BuOH); liquid phase), 2-cyanopyridine(2-CP; liquid), barrel process oil (B28AN; liquid phase) as a solvent,and carbon dioxide (CO₂; gas phase) supplied via a pressure raisingblower (not shown). The solid catalyst (CeO₂; solid phase) may be newlysupplied before the reaction or recovered from a catalyst separationcolumn 2. New 2-cyanopyridine is used at the start of the reaction.Alternatively, unreacted 2-cyanopyridine 19 (gas phase) separated andpurified in a dehydration agent separation column 3 and an amideseparation column 4, and 2-cyanopyridine 22 (liquid phase;2-cyanopyridine 26 via a solvent recovery column 24) regenerated from2-picolinamide purified in a water separation column 7, are reusable.

In a direct synthesis device for a carbonate ester usable in the presentinvention, one or both of CeO₂ and ZrO₂ are used as a solid catalyst.The synthesis device may be a flow reactor such as a batch reactor, asemi-batch reactor, a continuous tank reactor, a tube reactor or thelike.

(Temperature of the Reaction Solution)

The temperature of the reaction solution in the carbonate ester reactor1 is preferably 50 to 300° C. In the case where the temperature of thereaction solution is lower than 50° C., the reaction speed is low, andthe carbonate ester synthesis reaction or the hydration reaction with2-cyanopyridine does not advance almost at all. In this case, theproductivity of the carbonate ester tends to be low. In the case wherethe temperature of the reaction solution is higher than 300° C., thereaction speed of each reaction is high, but the carbonate ester iseasily decomposed or denatured and 2-picolinamide is easily reacted withan alcohol. Therefore, the yield of the carbonate ester tends to be low.The temperature of the reaction solution is more preferably 100 to 150°C. An ideal temperature of the reaction solution is considered to varyin accordance with the type or the amount of the solid catalyst, or theamount or the ratio of the materials (alcohol and 2-cyanopyridine).Thus, it is desirable to set the optimal temperature appropriately.Since the preferable temperature of the reaction solution is 100 to 150°C., it is desirable to pre-heat the materials (alcohol and2-cyanopyridine) with steam or the like on a stage before the carbonateester reactor.

(Reaction Pressure)

The reaction pressure in the carbonate ester reactor 1 is preferably 0.1to 20 MPa (absolute pressure). In the case where the reaction pressureis lower than 0.1 MPa (absolute pressure), a decompression device isrequired, which makes the facilities complicated and costly. Inaddition, a motive power energy to reduce the pressure is necessary,which decreases the energy efficiency. In the case where the reactionpressure is higher than 20 MPa, the hydration reaction with2-cyanopyridine does not easily advance, which decreases the yield ofthe carbonate ester. In addition, a motive power energy to raise thepressure is necessary, which decreases the energy efficiency. From thepoint of view of increasing the yield of the carbonate ester, thereaction pressure is more preferably 0.5 to 15 MPa (absolute pressure),and still more preferably 1.0 to 10 MPa (absolute pressure).

(Amount of 2-cyanopyridine)

2-cyanopyridine to be used for the hydration reaction is desirablyintroduced into the reactor before the reaction in a molar amount thatis 0.2 times or greater and 5 times or less of the theoretical molaramount of water generated as a by-product by the reaction of the alcoholand CO₂ as the materials. The molar amount of 2-cyanopyridine is moredesirably, 0.5 times or greater and 3 times or less, and especiallydesirably 0.8 times or greater and 1.5 times or less, of the theoreticalmolar amount of water generated as a by-product by the reaction of thealcohol and CO₂ as the materials. In the case where the molar amount of2-cyanopyridine is too small, the amount of 2-cyanopyridine contributingto the hydration reaction is small, which may undesirably decrease theyield of the carbonate ester. By contrast, in the case where the molaramount of 2-cyanopyridine is too large with respect to the alcohol as amaterial, the by-reaction of 2-cyanopyridine is undesirably increased.The ideal amounts of the alcohol and 2-cyanopyridine with respect to thesolid catalyst are considered to vary in accordance with the type or theamount of the solid catalyst, the type of the alcohol, or the ratio ofthe alcohol and 2-cyanopyridine. Thus, it is desirable to set theoptimal conditions appropriately.

(Separation of the Reaction Products)

Preferably, the separation of the reaction products is entirelyperformed by distillation. After the reaction in the carbonate esterreactor 1, a reaction solution 10 is transported to the catalystseparation column 2. From the bottom of the catalyst separation column2, the catalyst and the solvent (in this example, barrel process oil(B28AN) (liquid phase; 11)) are recovered. From the top of the catalystseparation column 2, CO₂ (12) and a mixture (13) of BuOH, dibutylcarbonate (DBC), 2-cyanopyridine and 2-picolinamide are recovered. Thecatalyst, the solvent and CO₂ that are recovered are recycled to thecarbonate ester reactor 1.

The mixture (13) recovered from the catalyst separation column 2 istransported to the dehydration agent separation column 3. From thebottom of the dehydration agent separation column 3, a mixture (14) of2-cyanopyridine and 2-picolinamide is recovered. From the top of thedehydration agent separation column 3, BuOH and DBC (15) are recovered.

The mixture (14) recovered from the bottom of the dehydration agentseparation column 3 is transported to the amide separation column 4.From the bottom of the amide separation column, 2-picolinamide (18) isrecovered. From the top of the amide separation column, the2-cyanopyridine (19) is recovered. The recovered 2-cyanopyridine isrecycled to the carbonate ester reactor 1. The 2-picolinamide (18)recovered from the bottom of the amide separation column 4 istransported to a nitrile regeneration reactor 6.

The BuOH and the DBC (15) recovered from the top of the dehydrationagent separation column 3 are transported to a carbonate ester recoverycolumn 5. From the bottom of the carbonate ester recovery column, DBC(16) is recovered. From the top of the carbonate ester recovery column,BuOH (17) is recovered. The recovered BuOH is recycled to the carbonateester reactor 1.

The 2-picolinamide (2-PA; 18) recovered from the amide separation column4 is transferred to the nitrile regeneration reactor 6 (second reactionportion) to be regenerated into 2-cyanopyridine.

(Second Reaction Step)

In the second reaction step, 2-cyanopyridine (2-CP) is generated by adehydration reaction of 2-picolinamide in the nitrile regenerationreactor 6. The production device used in the present invention (nitrileregeneration reactor 6) performs the dehydration reaction of2-picolinamide in the presence of a catalyst containing a carried basicmetal oxide and a solvent containing a specific solvent compound togenerate 2-cyanopyridine. There is no specific limitation on the form ofthe reaction. A flow reactor such as a batch reactor, a semi-batchreactor, a continuous tank reactor, a tube reactor or the like isusable. For the catalyst, a fixed bed, a slurry bed or the like isusable. The temperature of the nitrile regeneration reactor 6 isvariable in accordance with the form of the reaction. A reactiondistillation device having a decompression device attached thereto isused. Preferably, the distillation column is heated to have atemperature that is higher than the boiling point of water at thereaction pressure and is lower than the boiling point of the solvent atthe reaction pressure. As described above, the temperature of thereaction solution is adjusted to be higher than, or equal to, theboiling point of the solvent at the pressure reaction and lower than theboiling point of 2-picolinamide at the reaction pressure. With such anarrangement, the solvent partially gasified in the reaction system iscooled by a cooling device and returns to the reaction tube. Theby-product water is efficiently separated by distillation from thereaction solution and removed to the outside of the system. Therefore,the nitrile regeneration reaction advances at high speed.

Among 1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene as the specific solventcompounds, any of the three compounds having a relatively low boilingpoint other than 1,3,5-trimethoxybenzene may be used as a main componentof a solvent. In such a case, the solvent recovery column 24 may beprovided, so that the solvent is recovered efficiently. Namely, thesolvent recovery column 24 shown in FIG. 1 may be provided, so that afirst recovered solvent (21) recovered from the water separation column7 and also a second recovered solvent (25) separated from the2-cyanopyridine (22) in the solvent recovery column 24 are reusable.

The 2-cyanopyridine (22) may be recovered from the water separationcolumn 7 during the reaction or separated by distillation and recoveredafter the reaction. The recovered 2-cyanopyridine 22 is transported tothe carbonate ester reactor 1 and reused for the production of thecarbonate ester.

As described above, according to the present invention, a reactionproduct and a compound to be reused are separated from each other merelyby distillation, with no need of solid-liquid separation. Therefore,according to the present invention, a carbonate ester is producedefficiently with a simpler production device and a smaller number ofproduction steps.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of examples. The present invention is not limited to any of thefollowing examples. First, examples and comparative examples of methodfor producing cyanopyridine will be described.

Examples 1 Through 6

In examples 1 through 6, only a specific solvent compound was used asthe solvent to perform the dehydration reaction.

Example 1

SiO₂ (CARiACT, G-6, surface area: 535 m²/g; produced by Fuji SilysiaChemical Ltd.) for a carrier was sized to 100 mesh or less, andpre-baked at 700° C. for about 1 hour. Then, in order to cause Cs to becarried as an alkaline metal, an aqueous solution was prepared usingCs₂CO₃ (produced by Wako Pure Chemical Industries, Ltd.) such that thefinal amount of Cs metal to be carried would be 0.5 mmol/g, and SiO₂ wasimpregnated with the aqueous solution. Then, the resultant substance wasdried at 110° C. for about 6 hours and was baked at 500° C. for about 3hours. As a result, a Cs₂O/SiO₂ catalyst was obtained. An Na₂O/SiO₂catalyst used in some of comparative examples described below wasproduced by substantially the same method as the Cs₂O/SiO₂ catalyst.

Next, a 3-necked round-bottom flask was used as a reactor. A magneticstirrer, the Cs₂O/SiO₂ catalyst (1.0 g (Cs: 0.5 mmol)), 2-picolinamide(2-PA; 6.1 g (50 mmol); produced by Tokyo Chemical Industry Co., Ltd.),and 1,3-dimethoxybenzene (51.8 g (375 mmol); produced by Tokyo ChemicalIndustry Co., Ltd.) were introduced into the reactor.

A thermometer and an air-cooling tube containing 10 g of molecular sieve4A were attached to the reactor. A Liebig condenser was attached to atop end of the air-cooling tube. The resultant device was to be used asa reaction device.

Then, the reaction was performed in a state where the reaction solutionwas heated at the normal pressure and kept in a boiled state whileby-product water was adsorbed to the molecular sieve without beingreturned to the reactor.

The start of the reaction was set to the timing when the reactionsolution started to be boiled, and the reaction was continued for 24hours.

After the reaction, the temperature was cooled to room temperature. Thereaction solution was sampled and diluted two-fold with ethanol, and1-hexanol was added thereto as an internal standard substance. Theresultant substance was subjected to a qualitative analysis with GC-MS(gas chromatograph-mass spectrometer) and to a quantitative analysiswith FID-GC. As a result, 2-cyanopyridine was found to be generated asshown in Table 1. The yield of 2-cyanopyridine was 69.1 mol %, and thegeneration ratio of pyridine as a by-product was suppressed to 0.88 mol% (see Table 1).

Examples 2 and 3

In examples 2 and 3, the reaction was performed in substantially thesame manner as in example 1 with different specific solvent compounds.The results are shown in Table 1.

Example 4

A Cs₂O/SiO₂ catalyst was produced in the same step as in example 1.Next, a 3-necked round-bottom flask was used as a reactor. A magneticstirrer, the Cs₂O/SiO₂ catalyst (1.0 g (Cs: 0.5 mmol)), 2-picolinamide(2-PA; 6.1 g (50 mmol); produced by Tokyo Chemical Industry Co., Ltd.),and 1,3,5-trimethoxybenzene (176.6 g (1.05 mol; produced by TokyoChemical Industry Co., Ltd.) were introduced into the reactor.

Then, a thermometer was attached to the reactor. A distilling headhaving a thermometer attached thereto was attached to a top end of afirst air-cooling tube. A second air-cooling tube, a receiver, and avacuum pump were connected to the distilling head. The resultant devicewas to be used as a reaction distillation device. A ribbon heater waswound around the first air-cooling tube, so that the temperature of thefirst air-cooling tube would be adjustable. A cooling trap was cooledwith liquid nitrogen, so that gasified pyridine would be recovered.

Then, the pressure in the reaction distillation device was reduced bythe vacuum pump to 52.3 kPa (392 Torr). The first air-cooling tube washeated to 87° C., which was higher than the boiling point of water atthe reaction pressure and lower than the boiling point of1,3,5-trimethoxybenzene at the reaction pressure. The reaction solutionwas maintained in a boiled state at 229° C., which was higher than, orequal to, the boiling point of 1,3,5-trimethoxybenzene at the reactionpressure and lower than the boiling point of 2-picolinamide at thereaction pressure. The temperatures were adjusted in this manner, sothat the reaction was performed in a state where 1,3,5-trimethoxybenzenepartially gasified in the reaction system was cooled in the firstair-cooling tube and returned to the reactor while the by-product waterwas separated by distillation and removed to the outside of the systemwithout being returned to the reactor.

The start of the reaction was set to the timing when the reactionsolution started to be boiled, and the reaction was continued for 4hours.

After the reaction, the reaction solution was cooled to roomtemperature. The reaction solution was sampled and diluted two-fold withethanol, and 1-hexanol was added thereto as an internal standardsubstance. The resultant substance was subjected to a qualitativeanalysis with GC-MS (gas chromatograph-mass spectrometer) and to aquantitative analysis with FID-GC. As a result, 2-cyanopyridine wasfound to be generated as shown in Table 1. The yield of 2-cyanopyridinewas 53.1 mol %, and the generation ratio of pyridine as a by-product wassuppressed to 1.67 mol % (see Table 1).

Examples 5 and 6

In examples 5 and 6, the reaction was performed in substantially thesame manner as in example 1 with a mixture of specific solventcompounds. The results are shown in Table 2.

In examples 1 through 6, the aromatic nitrile compound (2-cyanopyridine)was generated at a high yield while the generation of pyridine as a mainby-product was suppressed as described below in detail.

Examples 7 Through 12

In each of examples 7 through 9 and 11, the dehydration reaction wasperformed in substantially the same manner as in embodiment 4 using asolvent containing a specific solvent compound and also diphenylether asanother component. As a result of these examples, it has been confirmedthat even in the case where a mixed solvent having a total amount of thefour specific solvent compounds of 20 to 60% by weight is used, a highnitrile selectivity (mol %) (amount of aromatic nitrile compound(mol)/(amount of pre-reaction aromatic amide compound (mol)−amount ofpost-reaction aromatic amide compound (mol))×100) is realized in adehydration reaction having a relatively short reaction time of 6 hoursor 12 hours (see Table 3). Namely, as shown in examples 7 through 9 and11 and the graph in FIG. 3, use of a mixed solvent containing 20% byweight or greater of 1,3-dimethoxybenzene, which was one of the specificsolvent compounds, realized a high nitrile selectivity of 80 mol % orhigher.

In examples 7 through 9 and 11 with a short reaction time, the yield ofthe aromatic nitrile compound (nitrile yield) is considered as not beingas high as in examples 1 through 6. However, in examples 10 and 12, inwhich only 1,3-dimethoxybenzene as a specific solvent compound was usedas the solvent, and the dehydration reaction was performed with areaction time of 6 hours or 12 hours, like in examples 7 through 9 usingthe mixed solvents; the yield of the aromatic nitrile compound wasgenerally equal to the yield in examples 7 through 9 (see Table 3). Inexample 1, the dehydration reaction was performed for a longer time of24 hours using only 1,3-dimethoxybenzene as the solvent, and a highnitrile yield of about 70% was realized. In consideration of theseresults, it is considered that even in a dehydration reaction using amixed solvent in examples 7 and thereafter, a high nitrile yield wouldbe realized in accordance with the reaction time.

Comparative Examples 1 Through 17

In the meantime, in comparative examples 1 through 17, a solventcontaining none of the four specific solvent compounds was used. Incomparative examples 10, 14 and 16, the dehydration reaction wasperformed in substantially the same manner as in example 4. In the othercomparative examples, the dehydration reaction was performed insubstantially the same manner as in example 1. As a result,2-cyanopyridine was produced from 2-picolinamide (see Table 4).

In comparative example 1 with a significantly longer reaction time of400 hours, an aromatic nitrile compound was generated at a high yield,and the generation of pyridine as a by-product was suppressed. However,the dehydration reaction requiring such a long reaction time is notsuitable to practical use. In comparative examples 2 and thereafter witha reaction time of 24 hours (only in comparative example 10, thereaction time was 12 hours), the nitrile yield was significantly lower,and the generation amount of pyridine with respect to the generationamount of the nitrile compound (2-cyanopyridine) was larger, than inexamples 1 through 6 having a reaction amount of 24 hours orsignificantly shorter than 24 hours.

The results in examples 1 through 12 and comparative examples 1 through17 are shown in Tables 1 through 4 below.

TABLE 1 Solvent Solvent Reaction Substrate Catalyst boiling amountsolution Reaction amount Catalyst amount point Molar temperaturesolution Example Substrate mmol type mol % Solvent ° C. ratio ° C. stateExample 1 2-PA 15 Cs₂O/SiO₂ 1.0 1,3- 217 25 215 Boiled DimethoxybenzeneExample 2 2-PA 15 Cs₂O/SiO₂ 1.0 1,2,3,4- 207 25 210 Boiledtetrahydronaphthalene Example 3 2-PA 15 Cs₂O/SiO₂ 1.0 1,2- 207 25 210Boiled Dimethoxybenzene Example 4 2-PA 50 Cs₂O/SiO₂ 1.0 1,3,5- 255 21229 Boiled Trimethoxybenzene 1st air- cooling Pyridine Reaction tubeNitrile generation 2-CP Nitrile/ pressure temperature ReactionDehydration yield ratio selectivity pyridine Example kPa Torr ° C. timeh method mol % mol % mol % mol %/mol % Example 1 101.3 760 — 24Molecular 69.1 0.88 — 79 sieve Example 2 101.3 760 — 24 Molecular 56.50.65 — 87 sieve Example 3 101.3 760 — 24 Molecular 54.6 0.46 — 119 sieveExample 4 52.3 392 87 4 Distillation and 53.1 1.67 — 32 removal atreduced pressure

TABLE 2 Solvent Solvent Substrate Catalyst boiling amount amountCatalyst amount point Solvent Molar Example Substrate mmol type mol %Solvent ° C. amount g ratio Example 5 2-PA 50 Cs₂O/SiO₂ 1.01,2,3,4-tetrahydronaphthalene/ 211 183 27 1,3-Dimethoxybenzene =50/50(wt %) Example 6 2-PA 50 Cs₂O/SiO₂ 1.0 1,3-Dimethoxybenzene/ 230183 24 1,3,5-Trimethoxybenzene = 50/50(wt %) Reaction Pyridine SolutionReaction Reaction Nitrile generation Nitrile/ temperature solutionpressure Reaction Dehydration yield ratio pyridine Example ° C. statekPa Torr time h method mol % mol % mol %/mol % Example 5 214 Boiled101.3 760 24 Molecular 62.8 0.77 82 sieve Example 6 233 Boiled 101.3 7604 Molecular 65.1 1.10 59 sieve

TABLE 3 Solvent Solvent Reaction Substrate Catalyst boiling amountsolution Reaction amount Catalyst amount point Solvent Molar temperaturesolution Example Substrate mmol type mol % Solvent ° C. amount g ratio °C. state Example 7 2-PA 50 Cs₂O/SiO₂ 1.0 1,3-Dimethoxybenzene/ 227 18324 195 Boiled Diphenyleter = 60/40 (wt %) Example 8 2-PA 50 Cs₂O/SiO₂1.0 1,3Dimethoxybenzene/ 234 183 24 195 Boiled Diphenyleter = 40/60 (wt%) Example 9 2-PA 50 Cs₂O/SiO₂ 1.0 1,3-Dimethoxybenzene/ 244 183 23 200Boiled Diphenyleter = 20/80 (wt %) Example 10 2-PA 50 Cs₂O/SiO₂ 1.01,3-Dimethoxybenzene 217 182 26 194 Boiled Example 11 2-PA 50 Cs₂O/SiO₂1.0 1,3-Dimethoxybenzene/ 227 183 25 195 Boiled Diphenyleter = 60/40 (wt%) Example 12 2-PA 50 Cs₂O/SiO₂ 1.0 1,3-Dimethoxybenzene 217 182 26 194Boiled 1st air- cooling Pyridine Reaction tube Nitrile generation 2-CPNitrile/ pressure temperature Reaction Dehydration yield ratioselectivity pyridine Example kPa Torr ° C. time h method mol % mol % mol% mol %/mol % Example 7 42.0 315 50 6 Distillation and 13.4 Below the100.0 — removal at detection limit reduced pressure Example 8 34.3 25750 6 Distillation and 14.4 Below the 95.8 — removal at detection limitreduced pressure Example 9 29.6 222 50 6 Distillation and 8.2 0.050 80.4164 removal at reduced pressure Example 10 53.6 402 50 6 Distillationand 14.4 0.079 99.9 183 removal at reduced pressure Example 11 42.0 31550 12 Distillation and 22.8 0.29 96.5 78 removal at reduced pressureExample 12 53.6 402 50 12 Distillation and 25.6 0.25 96.8 104 removal atreduced pressure

TABLE 4 Solvent Solvent Reaction Substrate Catalyst boiling amountsolution Reaction Comparative amount Catalyst amount point Molartemperature solution example Substrate mmol type mol % Solvent ° C.ratio ° C. state Comparative 2-PA 5 Na₂O/SiO₂ 1.0 Mesitylene 165 25 165Boiled example 1 Comparative 2-PA 5 Na₂O/SiO₂ 1.0 Mesitylene 165 25 165Boiled example 2 Comparative Pyrazinamide 15 Cs₂O/SiO₂ 1.0 Mesitylene165 25 165 Boiled example 3 Comparative 2-PA 15 Na₂O/SiO₂ 1.03,4-Dimethoxytoluene 218 25 223 Boiled example 4 Comparative 2-PA 15Cs₂O/SiO₂ 1.0 1-tert-Butyl-3,5- 202 25 204 Boiled example 5Dimethylbenzene Comparative 2-PA 15 Cs₂O/SiO₂ 1.0 Cyclohexylbenzene 23625 202 Not boiled example 6 Comparative 2-PA 15 Cs₂O/SiO₂ 1.03,5-Dimethylanisole 193 25 195 Boiled example 7 Comparative 2-PA 15Na₂O/SiO₂ 1.0 3-Methylanisole 177 25 180 Boiled example 8 Comparative2-PA 15 Cs₂O/SiO₂ 1.0 4-tert-Butylanisole 222 25 202 Not boiled example9 Comparative 2-PA 50 Cs₂O/SiO₂ 1.0 Dihenyl Sulfide 296 25 182 Boiledexample 10 Comparative 2-PA 15 Cs₂O/SiO₂ 1.0 Dihenyl Sulfide 296 25 202Not boiled example 11 Comparative 2-PA 7.5 Na₂O/SiO₂ 1.0 Amylbenzene 20525 207 Boiled example 12 Comparative 2-PA 15 Cs₂O/SiO₂ 1.01-Methylnaphthalene 241 25 203 Not boiled example 13 Comparative 2-PA 15Cs₂O/SiO₂ 1.0 1-Methoxynaphthalene 271 25 202 Not boiled example 14Comparative 2-PA 15 Cs₂O/SiO₂ 1.0 Diamyl Ether 186 25 189 Boiled example15 Comparative 2-PA 15 Cs₂O/SiO₂ 1.0 Dibenzyl Ether 298 25 201 Notboiled example 16 Comparative 2-PA 15 Cs₂O/SiO₂ 1.0 Diethylene GlycolDiethyl 188 25 191 Boiled example 17 Ether 1st air- cooling PyridineReaction tube Nitrile generation 2-CP Nitrile/ Comparative pressuretemperature Reaction Dehydration yield ratio (*1) selectivity pyridine(*2) example kPa Torr ° C. time h method mol % mol % mol % mol %/mol %Comparative 101.3 760 — 400 Molecular sieve 79.2 0.34 — 232 example 1Comparative 101.3 760 — 24 Molecular sieve 9.9 Below the — — example 2detection limit Comparative 101.3 760 — 24 Molecular sieve 2.70 Belowthe — — example 3 detection limit Comparative 101.3 760 — 24 Molecularsieve 13.3 1.88 — 7 example 4 Comparative 101.3 760 — 24 Molecular sieve20.0 3.60 — 6 example 5 Comparative 101.3 760 — 24 Molecular sieve 4.821.52 — 3 example 6 Comparative 101.3 760 — 24 Molecular sieve 0.49 0.12— 4 example 7 Comparative 101.3 760 — 24 Molecular sieve 2.54 Below the— example 8 detection limit Comparative 101.3 760 — 24 Molecular sieve16.0 0.49 — 32 example 9 Comparative 6.13 46 45 12 Distillation and 18.30.35 — 53 example 10 removal at reduced pressure Comparative 101.3 760 —24 Molecular sieve 17.4 1.28 — 14 example 11 Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 12 reactionsolution is blackened by the by-product Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 13 reactionsolution is blackened by the by-product Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 14 reactionsolution is blackened by the by-product Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 15 reactionsolution is blackened by the by-product Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 16 reactionsolution is blackened by the by-product Comparative 101.3 760 — 24Molecular sieve Non-adoptable because the — — example 17 reactionsolution is blackened by the by-product (*1) In comparative example 3,pyrazine generation ratio (mol %) (*2) In comparative example 3,nitrile/pyrazine (mol %/mol %)

As described above, the dehydration reaction in examples 1 through 12using a specific solvent compound as a solvent resulted in generatingthe aromatic nitrile compound as a target compound at a high yield whilesuppressing the generation of a by-product such as pyridine or the like.Especially in examples 1 through 5 and 7 through 12, in which thetemperature of the reaction solution was adjusted to the range of 170°C. to 230° C., a high yield of the nitrile compound and the reduction ofthe generation of the by-product were both confirmed be realized.

By contrast, the comparative examples, in which a solvent containingnone of the specific solvent compounds was used, resulted in a low yieldof the aromatic nitrile compound (see FIG. 4, which shows the results ofthe examples and the comparative examples exhibiting a relatively highyield). In some of the comparative examples, the generation of pyridinewas suppressed. However, even in these comparative examples, the nitrideyield was low. In comparative example 1, the nitrile yield was high, butthe required reaction time was too long. Thus, comparative example 1 wasinferior to the examples.

For evaluation of the catalysts, control tests were performed amongwhich only the type of the catalyst was different. The catalysts usedwere the catalysts usable for the dehydration reaction. In the controltests, the type of the solvent was different from that in example 1 andthe like. The tests were performed under the reaction conditionssuitable to the boiling point of the solvent. The results are shown inTable 5.

TABLE 5 Solvent Solvent Reaction Substrate Catalyst boiling amountsolution Reference amount Catalyst amount point Molar temperatureexample Substrate mmol type mol % Solvent ° C. ratio ° C. Reference 2-PA5 Li₂O/SiO₂ 1.0 Mesitylene 165 25 165 example 1 Reference 2-PA 5Na₂O/SiO₂ 1.0 Mesitylene 165 25 165 example 2 Reference 2-PA 5 K₂O/SiO₂1.0 Mesitylene 165 25 165 example 3 Reference 2-PA 5 Rb₂O/SiO₂ 1.0Mesitylene 165 25 165 example 4 Reference 2-PA 5 Cs₂O/SiO₂ 1.0Mesitylene 165 25 165 example 5 Reference 2-PA 5 CaO/SiO₂ 1.0 Mesitylene165 25 165 example 6 Reference 2-PA 5 CeO₂ 1.0 Mesitylene 165 25 165example 7 Reference 2-PA 5 MoO₃/SiO₂ 1.0 Mesitylene 165 25 165 example 8Pyridine Reaction Reaction Nitrile generation Reference solutionpressure Reaction Dehydration yield ratio example state kPa Torr time hmethod mol % mol % Reference Boiled 101.3 760 24 Molecular sieve 2.91Below the example 1 detection limit Reference Boiled 101.3 760 24Molecular sieve 9.9 Below the example 2 detection limit Reference Boiled101.3 760 24 Molecular sieve 16.0 Below the example 3 detection limitReference Boiled 101.3 760 24 Molecular sieve 17.8 Below the example 4detection limit Reference Boiled 101.3 760 24 Molecular sieve 18.2 Belowthe example 5 detection limit Reference Boiled 101.3 760 24 Molecularsieve 1.17 Below the example 6 detection limit Reference Boiled 101.3760 24 Molecular sieve 11.0 Many example 7 by-product peaks ReferenceBoiled 101.3 760 24 Molecular sieve 1.54 Below the example 8 detectionlimit

As described above, it has especially been confirmed that in the casewhere Cs₂O, Rb₂O, K₂O or Na₂O is used as the catalyst in the dehydrationreaction according to the present invention, the aromatic nitrilecompound is obtained selectively at a high yield.

Example 13

A 5 L 3-necked round-bottom flask was used as a reactor. A magneticstirrer, the Cs₂O/SiO₂ catalyst (10 g (Cs: 5 mmol)), 2-picolinamide (61g (0.5 mol); produced by Tokyo Chemical Industry Co., Ltd.), and1,3-dimethoxybenzene (1727 g (12.5 mol); produced by Tokyo ChemicalIndustry Co., Ltd.) were introduced into the reactor. A reactiondistillation device was structured in substantially the same manner asin example 1.

The reaction was performed under the same conditions as in example 2 toobtain a reaction solution containing 38.5 g of 2-cyanopyridine.

The reaction distillation device was used continuously to distill thereaction solution at a pressure of 1.3 kPa to obtain 33.5 g of2-cyanopyridine. As a result of an analysis performed with FID-GC, thepurity thereof was 99.9%.

It has been confirmed that in the case where, as described above,1,3-dimethoxybenzene is used and the temperature of the reactionsolution is adjusted by pressure control, the reaction speed issignificantly improved to shorten the reaction time, the target compoundis obtained selectively at a high yield, and the aromatic nitrilecompound is recovered easily.

Example 14

Now, examples of method for producing a carbonate ester usingcyanopyridine (carbonate ester generation reaction) will be described.The 2-cyanopyridine obtained in example 13 was used. First, commerciallyavailable CeO₂ (impurity concentration: 0.02% or lower) was baked at600° C. for 3 hours in an air atmosphere to obtain a powdery solidcatalyst.

A magnetic stirrer, the solid catalyst (0.17 g (1 mmol)), butanol (7.4 g(100 mmol); produced by Wako Pure Chemical Industries, Ltd.), barrelprocess oil B-28AN (5 g) as the solvent, and 2-cyanopyridine (5.2 g (50mmol)) were introduced into a 190 mL autoclave (reactor). The air in theautoclave was purged three times with CO₂, and then CO₂ was introducedinto the autoclave such that the pressure would be 5 MPa. Thetemperature of the autoclave was raised to 132° C. by a band heater anda hot stirrer. The timing when the temperature reached the targettemperature was set as the reaction start time. During the reaction, thepressure reached 8 MPa. The reaction was continued for 24 hours at thetemperature of the reaction solution of 132° C. as described above.Then, the autoclave was cooled with water. When the autoclave was cooledto room temperature, the pressure in the autoclave was reduced. Thesolution in the autoclave was diluted two-fold with acetone, and1-hexanol was added thereto as an internal standard substance. Theresultant substance was analyzed with FID-GC. Dibutyl carbonate wasobtained in this manner.

Examples 15 Through 47

In examples 15 through 47, a carbonate ester was obtained from analcohol and CO₂ using 2-cyanopyridine under the conditions in which atleast one of presence/absence of the solvent, the type of the solvent,the amount of the solvent, the reaction time, the type of the alcohol(substrate), the concentration of the alcohol (substrate), the type ofthe catalyst, and the amount of the catalyst was different from that inexample 14. Specifically, the conditions different from those in example14 were the type and the amount of the solvent in examples 15 through18, 41 and 45 through 47 (regarding the solvent, “−” indicates that nosolvent was used), the reaction time in examples 18 through 21, 23through 30, 33 through 39, 43 and 45 through 47, the value of thealcohol/2-cyanopyridine as the materials in examples 23 through 28, 35,37, 42 and 45 through 47, the amount of the catalyst in examples 25through 30, 35, 37 and 45 through 47, the type of the catalyst inexamples 31 through 34, the temperature of the reaction solution inexamples 37 through 47, the reaction pressure in examples 43 and 44, andthe type, the amount and the like of the alcohol as the material inexamples 35 through 47.

Table 6 below shows the results of the examples of production of thecarbonate ester.

TABLE 6 Nitrile/ theoretically Substrate 2-CP generated Catalyst amountamount water Molar amount Solvent Substrate [mmol] [mmol] ratio Catalysttype [mmol] Example 14 High-boiling point solvent BuOH 100 50 1.0CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 barrel process oil (using 5 gof B-28AN) Example 15 High-boiling point solvent BuOH 100 50 1.0CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 barrel process oil (using 15 gof B-28AN) Example 16 High-boiling point solvent BuOH 100 50 1.0CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 barrel process oil (using 5 gof B-30) Example 17 High-boiling point solvent BuOH 100 50 1.0CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 barrel process oil (using 15 gof B-30) Example 18 High-boiling point solvent BuOH 100 50 1.0CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 barrel process oil (using 5 gof B-30) Example 19 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for3 h 1.0 Example 20 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3h 1.0 Example 21 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h1.0 Example 22 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h1.0 Example 23 — BuOH 20 100 10 CeO₂(HSA-20) baked at 600° C. for 3 h1.0 Example 24 — BuOH 100 100 2.0 CeO₂(HSA-20) baked at 600° C. for 3 h1.0 Example 25 — BuOH 200 50 0.50 CeO₂(HSA-20) baked at 600° C. for 3 h0.5 Example 26 — BuOH 300 50 0.33 CeO₂(HSA-20) baked at 600° C. for 3 h0.3 Example 27 — BuOH 20 100 10 CeO₂(HSA-20) baked at 600° C. for 3 h10.0 Example 28 — BuOH 20 100 10 CeO₂(HSA-20) baked at 600° C. for 3 h20.0 Example 29 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h2.0 Example 30 — BuOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h3.0 Example 31 — BuOH 100 50 1.0 CeO₂(HSA-5) un-baked 1.0 Example 32 —BuOH 100 50 1.0 CeO₂(HSA-5) baked at 600° C. for 3 h 1.0 Example 33 —BuOH 100 50 1.0 CeO₂(HSA-5) baked at 600° C. for 3 h 1.0 Example 34 —BuOH 100 50 1.0 CeO₂(first rare element) baked at 600° 1.0 C. for 3 hExample 35 — EtOH 20 100 10 CeO₂(HSA-20) baked at 600° C. for 3 h 10.0Example 36 — EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0Example 37 — EtOH 20 100 10 CeO₂(HSA-20) baked at 600° C. for 3 h 10.0Example 38 — EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0Example 39 — EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0Example 40 — EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0Example 41 High-boiling point solvent EtOH 100 50 1.0 CeO₂(HSA-20) bakedat 600° C. for 3 h 1.0 barrel process oil (using 5 g of B-30) Example 42— EtOH 100 150 3.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 Example 43— EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 Example 44 —EtOH 100 50 1.0 CeO₂(HSA-20) baked at 600° C. for 3 h 1.0 Example 45High-boiling point solvent Ethyleneglycol 50 50 1.0 CeO₂(HSA-20) bakedat 600° C. for 3 h 2.0 barrel process oil (using 5 g of B-30) Example 46High-boiling point solvent 1,2-Propanediol 50 50 1.0 CeO₂(HSA-20) bakedat 600° C. for 3 h 2.0 barrel process oil (using 5 g of B-30) Example 47High-boiling point solvent 1,3-Propanediol 50 50 1.0 CeO₂(HSA-20) bakedat 600° C. for 3 h 2.0 barrel process oil (using 5 g of B-30) PicolinicPyridinimidic Carbamic acid ester acid ester acid ester Reactiongeneration generation generation Dialkyl solution Reaction Reactionamount as amount as amount as carbonate temperature pressure timeby-product by-product by-product yield ° C. [MPa] [h] mol % mol % mol %mol % Example 14 132 8 24 2.1 0.35 Below the 52.5 detection limitExample 15 132 8 24 1.0 0.20 Below the 41.0 detection limit Example 16132 8 24 1.7 0.30 Below the 55.1 detection limit Example 17 132 8 24 1.30.21 Below the 44.5 detection limit Example 18 132 8 4 0.23 0.16 Belowthe 38.0 detection limit Example 19 132 8 4 0.35 0.14 Below the 46.5detection limit Example 20 132 8 12 0.90 0.29 Below the 56.7 detectionlimit Example 21 132 8 16 1.1 0.35 Below the 58.7 detection limitExample 22 132 8 24 1.8 0.44 Below the 63.5 detection limit Example 23132 8 16 0.19 0.40 Below the 25.0 detection limit Example 24 132 8 161.5 0.68 Below the 65.9 detection limit Example 25 132 8 16 1.8 0.16Below the 45.1 detection limit Example 26 132 8 16 3.8 0.18 Below the32.5 detection limit Example 27 132 8 4 0.80 0.80 Below the 60.1detection limit Example 28 132 8 4 2.0 0.70 Below the 72.9 detectionlimit Example 29 132 8 4 0.45 0.11 Below the 49.8 detection limitExample 30 132 8 4 0.61 0.15 Below the 54.1 detection limit Example 31132 8 24 1.8 3.1 Below the 33.0 detection limit Example 32 132 8 24 2.00.42 Below the 67.1 detection limit Example 33 132 8 4 0.29 0.17 Belowthe 42.8 detection limit Example 34 132 8 4 0.19 0.15 Below the 35.8detection limit Example 35 132 8 4 1.4 0.69 1.0 69.1 Example 36 132 8 40.51 0.14 0.41 56.8 Example 37 120 8 4 0.59 0.32 0.48 66.0 Example 38120 8 4 0.05 0.03 0.080 44.5 Example 39 110 8 0.03 0.01 Below the 33.9detection limit Example 40 110 8 24 0.43 0.16 0.40 57.6 Example 41 110 824 0.28 0.49 2.2 65.0 Example 42 110 8 24 0.45 0.22 0.37 63.0 Example 43110 1 4 0.13 0.12 0.10 38.9 Example 44 110 1 24 1.9 1.6 1.7 58.5 Example45 130 8 1 0.45 0.21 Below the 99.1 detection limit Example 46 140 8 10.40 0.20 Below the 99.2 detection limit Example 47 140 8 1 0.45 0.22Below the 99.0 detection limit

As described above, in examples 14 through 47, it has been confirmedthat the carbonate ester is obtained at a high yield within a shortreaction time of 24 hours or shorter while the hydration reaction of anaromatic cyano compound with the by-product water was advanced at thesame time as the carbonate ester generation reaction.

Example 48

Now, an example of recovery of the catalyst from the carbonate esterreaction solution will be described. The carbonate ester was produced byuse of the production device shown in FIG. 1. First, commerciallyavailable CeO₂ (impurity concentration: 0.02% or lower) was baked at600° C. for 3 hours in an air atmosphere to obtain a powdery solidcatalyst.

The solid catalyst (1.72 g (10 mmol)), butanol (74.1 g (1 mol); producedby Wako Pure Chemical Industries, Ltd.), barrel process oil B-28AN (50g) as the solvent, and 2-cyanopyridine (52.1 g (0.5 mol)) wereintroduced into a 1.9 L autoclave (reactor) with a stirrer. The air inthe autoclave was purged three times with CO₂, and then CO₂ wasintroduced into the autoclave such that the pressure would be 5 MPa. Thetemperature of the autoclave was raised to 132° C. by a ceramic heaterwhile the substances in the autoclave were stirred. The timing when thetemperature reached the target temperature was set as the reaction starttime. During the reaction, the pressure reached 8 MPa.

The reaction was continued for 24 hours at the temperature of thereaction solution of 132° C. as described above. Then, the pressure inthe autoclave was returned to the atmospheric pressure. The reactionsolution was introduced to a middle portion of a distillation columnhaving a reduced pressure of 2.7 kPa, and simple distillation wasperformed. From the top of the distillation column, a mixture of BuOH,dibutyl carbonate, 2-cyanopyridine and 2-picolinamide was recovered.From the bottom of the distillation column, the catalyst and barrelprocess oil were recovered.

The catalyst and the solvent recovered above, butanol (74.1 g (1 mol);produced by Wako Pure Chemical Industries, Ltd.), and 2-cyanopyridine(52.1 g (0.5 mol)) were introduced into a 1.9 L autoclave (reactor) witha stirrer. The air in the autoclave was purged three times with CO₂, andthen CO₂ was introduced into the autoclave such that the pressure wouldbe 5 MPa. The temperature of the autoclave was raised to 132° C. by aceramic heater while the substances in the autoclave were stirred. Thetiming when the temperature reached the target temperature was set asthe reaction start time. During the reaction, the pressure reached 8MPa. After the reaction was continued for 24 hours, the autoclave wascooled with water. When the autoclave was cooled to room temperature,the pressure in the autoclave was reduced, and a part of the reactionsolution was sampled. The sampled reaction solution was diluted two-foldwith acetone, and 1-hexanol was added thereto as an internal standardsubstance. The resultant substance was analyzed with FID-GC. As aresult, the yield of dibutyl carbonate was 54 mol %.

Then, the reaction solution was distilled in the order shown in FIG. 1to obtain 40 g of dibutyl carbonate. An analysis with FID-GC showed thatthe purity was 99.9%.

As can be seen, it has been confirmed that even in the case where thecatalyst once used is recovered and used again for the carbonate estergeneration reaction, the carbonate ester is obtained at a high yield.

As described above, it has been confirmed that also in the carbonateester generation reaction, in the case where a solvent having a boilingpoint higher than that of aromatic carboamide is used, the componentsmay be separated from each other merely by distillation with no need ofthe step of solid-liquid separation of the catalyst. Thus, an efficientprocess is realized.

Preferable embodiments of the present invention have been describedabove in detail with reference to the attached drawings. The presentinvention is not limited to any of the embodiments. A person of ordinaryskill in the art of the present invention would obviously conceive anyof various altered or modified examples within the technological scopedefined by the claims, and such altered or modified examples areconstrued as being duly encompassed in the technological scope of thepresent invention.

REFERENCE SIGNS LIST

-   1 Carbonate ester reactor-   2 Catalyst separation column-   3 Dehydration agent separation column-   4. Amide separation column-   5 Carbonate ester recovery column-   6 Nitrile regeneration reactor-   7 Water separation column-   8 Decompression pump

What is claimed:
 1. A method for producing an aromatic nitrile compound,comprising: a dehydration reaction of dehydrating an aromatic amidecompound; wherein the dehydration reaction uses a solvent comprising1,2,3,4-tetrahydronaphthalene and optionally 1,2-dimethoxybenzene,1,3-dimethoxybenzene, 1,3,5-trimethoxybenzene, or mixtures thereof; anda catalyst comprising cesium.
 2. A method for producing a carbonateester, comprising: a first reaction step including a carbonate estergeneration reaction of reacting an alcohol and carbon dioxide in thepresence of an aromatic nitrile compound to generate a carbonate esterand water, and a hydration reaction of hydrating the aromatic nitrilecompound with the generated water to generate an aromatic amidecompound; and a second reaction step of, after the aromatic amidecompound is separated from a reaction system of the first reaction step,regenerating the aromatic amide compound into an aromatic nitrilecompound by a dehydration reaction of dehydrating the aromatic amidecompound in a solvent comprising 1,2,3,4-tetrahydronaphthalene andoptionally 1,2-dimethoxybenzene, 1,3-dimethoxybenzene,1,3,5-trimethoxybenzene, or mixtures thereof; by use of a catalystcomprising cesium; wherein at least a part of the aromatic nitrilecompound regenerated in the second reaction step is used in the firstreaction step.
 3. A method for producing a carbonate ester, comprising:a first reaction step including a carbonate ester generation reaction ofreacting an alcohol and carbon dioxide in the presence of an aromaticnitrile compound to generate a carbonate ester and water, and ahydration reaction of hydrating the aromatic nitrile compound with thegenerated water to generate an aromatic amide compound; and a secondreaction step of, after the aromatic amide compound is separated from areaction system of the first reaction step, regenerating the aromaticamide compound into an aromatic nitrile compound by a dehydrationreaction of dehydrating the aromatic amide compound in a solvent formedof only one or a plurality of substances selected from1,2,3,4-tetrahydronaphthalene, 1,2-dimethoxybenzene,1,3-dimethoxybenzene and 1,3,5-trimethoxybenzene, said solvent at leastcomprising 1,2,3,4-tetrahydronaphthalene; by use of a catalystcomprising cesium; wherein at least a part of the aromatic nitrilecompound regenerated in the second reaction step is used in the firstreaction step.